1. Field of the Invention
The present invention relates to a boundary acoustic wave device using a boundary acoustic wave propagating between a first medium and a second medium and a method for manufacturing the same. In particular, the present invention relates to a boundary acoustic wave device in which an IDT electrode disposed between the first medium and the second medium is defined by laminated metal films including at least an Au layer defining a main electrode layer and a method for manufacturing the same.
2. Description of the Related Art
Boundary acoustic wave devices are previously known as devices used as resonators and band pass filters. The boundary acoustic wave device has a structure in which an IDT electrode is disposed at the interface between a first medium and a second medium. In the boundary acoustic wave device, a boundary acoustic wave propagating along the interface is used. Therefore, the boundary acoustic wave device can be mechanically supported at surfaces opposite to the interface between the first medium and the second medium. Consequently, a simplified and small-sized package structure can be achieved.
An example of the boundary acoustic wave device is disclosed in WO2004/070946. In the boundary acoustic wave device described in WO2004/070946, an IDT electrode is formed by using Au, Ag, Cu, or Al or an alloy thereof. Furthermore, it is described that in order to improve the adhesion of the IDT electrode to a medium or to improve the electric power withstanding performance, a second electrode layer made of another metal material, e.g., Ti, Cr, or NiCr, may be laminated on at least one surface of the electrode layer made of Au, Ag, Cu, or Al or an alloy thereof.
As is described in WO2004/070946, IDT electrodes primarily made of various metals, e.g., Au, Ag, Cu, or Al or an alloy thereof, are known. Moreover, structures in which second electrode layers made of other metal materials are laminated on the electrode layers made of the metals are also known. However, such structures in which second electrode layers made of other metal materials are laminated have been used for improving the adhesion of the IDT electrodes or improving the electric power withstanding performance, as described above.
On the other hand, where the boundary acoustic wave devices are used as resonators and filters, not only the improvement of the electric power withstanding performance, but also improvements of frequency characteristics, e.g., an insertion loss, in a pass band have been in high demand.